The present invention relates to a method and apparatus for checking an earth effect of a tire and, more particularly, to a tire earth effect checking method and apparatus which can highly reliably check the earth effect of a tire.
In recent years, in order to improve fuel consumption and drainage performance by lowering rolling resistance, rubber mixed with a large amount of silica has been used for the rubber portion of the tread of a pneumatic tire. With an increase in the amount of silica, the amount of carbon decreases to thereby lower electrical conductivity with respect to a road surface. As a result, the vehicles keep static electricity, which can badly affect noise interference with a radio and the like, and vehicle fire.
To eliminate static electricity from the vehicle, there are proposed a lot of tires in which the rubber portion of the tread consists of a cap tread rubber layer mixed with a large amount of silica, and a under tread rubber layer, disposed inwardly thereof, mixed with a large amount of carbon, and an earth rubber part for connecting the under tread rubber layer and a road surface is provided in the cap tread rubber layer so that the earth rubber part is exposed on the surface of the cap tread rubber layer. The static electricity is discharged from the vehicle through the earth rubber part to a road surface.
In order to check the effect of the earth rubber part of such tires, there is disclosed a technology in Published Unexamined Japanese Patent Application No. 2002-337246, which measures an electric resistance value of the tire by applying a voltage between the rim of a wheel on which the tire is mounted, and the tread surface on which the earth rubber part exposes. The electrical conductivity of the tire (the earth effect of the earth rubber part) is judged on the basis of the electric resistance value.
However, the above technology requires a troublesome operation of assembling the tire to the rim of a wheel, and the contact state of an electrode which is electrically connected to the tread surface varies due to patterns of the tread surface. Therefore, there is variation in the electric resistance value obtained, and a problem arises such as a decrease in reliability of the earth effect.